ENERGY-LOSS DISTRIBUTIONS FOR 2.5-MEV HE+ IONS INCIDENT ON SI SINGLE-CRYSTALS

The energy distributions for 2.5-MeV He+ ions incident on thin Si single crystals are studied. Detailed angular scans are taken through the 110 and 100 axial directions along the {111} and {110} planar directions as well as perpendicular to the planar directions for Si(110) (0.74- and 1.4-μm-thick) and Si(100) (0.75-μm-thick) samples, respectively. Complex structures in the distributions are observed throughout the angular scans. The experimental distributions are reasonably well reproduced by a Monte Carlo simulation using the semiclassical approximation [N. M. Kabachnik, V. N. Kondratev, and O. V. Chumanova, Phys. Status Solidi B 145, 103 (1988)] for energy loss to core electrons and the two-component free-electron-gas model for energy loss to valence electrons. Systematic deviations between theory and experiment are observed and discussed in terms of an increased penetration depth necessary for He+ ions to become fully ionized when channeled. © 1995 The American Physical Society.